In a conventional air-operated power tool such as an angle wrench, air enters by means of a hose which is connected to the plant air supply and through a simple throttle or control valve. The air enters a rotary vane motor and causes the rotor of that motor to rotate. It is a characteristic of rotary vane motstors to operate at high speed and low torque. Therefore, the output shaft of the motor in an angle wrench is usually connected to one or more planetary gear sets for the purpose of multiplying the torque and reducing the speed. In turn, the output shaft of the planetary gear set is connected to a right angle gear set, the output of which has a square drive which can be used to mount a socket for driving a fastener.
In some assembly operations, it is desirable to provide a means for shutting the tool off automatically when a preset torque is reached. The apparatus described in the preferred embodiment of this invention is such a device. It is intended to sense when the air motor rotor is approaching stall and shut off the air supply to the motor. By varying the supply air pressure, gear ratio, and motor size, any torque can be produced. Assuming the air supply pressure can be maintaining at a reasonably constant level, the output for shut-off torque may be controlled within suitable limits for many assembly fastener applications.